Share 'Great Web 2.0 Tools'

I attended several sessions at NECC on Web 2.0 tools. Many were tools I've used before, or I've seen but not used, or heard of but not looked at - and some I'd never heard of. But together they make such a great collection that I felt the need to share with others, as I have never seen all of these listed together in one place. No doubt you've seen many of these before, but I hope you find somet…